This invention relates to demand or impulse ink jets of the type wherein a droplet of ink is ejected from an orifice in response to a command at a frequency which can vary as the frequency of the commands.
In many applications, it is desirable to operate a demand ink jet apparatus with a high frequency, e.g., 9 to 10 KHz. In many instances, it is difficult to achieve a stable high frequency operation of an ink jet. Such stable, high frequency operation is, in part, difficult to achieve because of the nature of filling of the chamber prior to firing of the demand ink jet. Specifically, in the typical demand ink jet, filling of the chamber is a function of the manner in which the chamber expands which, in turn, may be a function of the operating characteristics of the transducer associated with the chamber.
Where an ink jet chamber is filled as the transducer is relaxed, the manner in which the chamber is filled is a function of the fall time of the pulse or signal which energizes the transducer. Where the fall time is extended, i.e., the pulse decays slowly over a period of time, the chamber will fill gradually over an extended period of time making high frequency operation difficult. On the other hand, a rapid fall time will produce rapid filling of the chamber. It should, therefore, be appreciated that variations in the fall time may have a substantial effect on the filling action of the chamber which, in turn, will greatly affect the position of the meniscus within the orifice of the chamber. This can result in unstable operation (e.g., satellites, air ingestion or off line droplets) at high frequencies where the position of the meniscus varies as a function of time. Of course, problems can be compounded where a plurality of ink jets are utilized where the fall times of the driving pulses of the ink jets vary from one jet to another.